Sky is the limit – say the zoologists studying the extremely small frogs of the genus Brachycephalus. In case of these animals, there seems to be no evolutionary limit. Another species has just been discovered. – There may be many more – think the scientists.
All because we are dealing with very small animals that need a small area to live. There are many endemics in the world, animals confined to a very small territory (in some cases – the fault of man), but these amphibians mark a new meaning of the term “limited area” among vertebrates.
Brachycephalus are tiny frogs. They have no Polish name, only the species Brachycephalus didactylus uses the still unofficial Polish name brazilian biped. So perhaps all these frogs should be called “two-toed” (from the two toes in the forelegs in some species; the hind legs of these frogs are provided with three toes in many cases).
Frogs the size of a fingernail
These micro-frogs are no larger than our thumb, and some of them reach the size of a fingernail from our thumb, and are therefore no larger than some insects.
These animals are by no means the smallest among amphibians – here the record has recently been held by Paedophryne amauensis (without a Polish name), belonging to the narrow-legged frogs. In 2009 Americans discovered it near the village of Amau (hence the name) in Papua New Guinea. This tiny frog measures 7.7 mm, which hereby makes it not only the smallest amphibian, but even the world’s smallest vertebrate. The Papua New Guinea frog took this record away from a tiny fish from Sumatra, and in the world of amphibians – from the Brazilian two-toed frog, which reaches a length of about 1 cm.
Frogs glow like in “Avatar”
So we are dealing with inhabitants of a micro-world that we barely notice. And this despite the fact that the two-toed frogs of the genus Brachycephalus are often very brightly coloured – mainly orange or yellow, hence in English they are called “pumpkin toadlets“toadlets. What is more, they are glowing frogs. The fluorescence of their skin is still a mystery to this day, probably in some way used for communication. In any case, these amphibians are like organisms from the movie “Avatar“.
These colorful amphibians sneak among the leaves and litter. They are so tiny that they need a very small area to live, not even a single forest, but a fragment of it. They don’t travel, they don’t move very far, and sometimes it’s not clear if they still exist. Take the species Brachycephalus vertebralis, discovered in 1998 on the Bocaina forest floor in Brazil. It was seen that one and only time then, and was lost like a stone in water. A search with specialized equipment for the frog yielded no results. It was lost.
Lots of animals in one Brazil
Genus Brachycephalus is today 35 described species of tiny frogs. This is not a record – this one belongs to the so-called rain frogs of the genus Pristimantis. It includes more than 500 species of amphibians living from Honduras to Argentina and the Caribbean, of which 11 more were discovered in 2019 alone. Well, that’s right – from Honduras to Argentina, that’s a huge area of the Americas.
In the case of all the frogs in the genus Brachycephalus we are not even dealing with a single country, but only a fragment of it – this is the southeastern areas of Brazil. So this is a situation absolutely unprecedented in the world of vertebrates. Dozens or even more species of one genus live in one forest range of one country in the world.
Starting in 2018, a group of Brazilian researchers from São Paulo State University studied these frogs in Brazil’s Atlantic coast forests. These are not equatorial rainforests, they are a completely different type of subtropical vegetation called Mata Atlântica, or so-called Atlantic forest. A unique and found only here thicket, hence unique and found only here are these amphibians.
The research concerned the species Brachycephalus ephippiumwhich, as for this group of animals, is extremely common and found in as many as four Brazilian states, admittedly tiny, but still – Espiritiu Santo, Rio de Janeiro, Minas Gerais and São Paulo (in the case of the last two – only in their fragments). So here it was relatively easy to find frogs to study, and we already know that it is not an easy art.
Two-toed frogs are astonishing
Brazilian herpetologists have captured 276 representatives of this species. They added museum specimens caught over a 200 kilometer area. They studied the DNA code and mating behavior of the males, as well as appearance and size. The differences turned out to be colossal. So much so, that already at this stage of research, a completely new species was distinguished Brachycephalus rotenbergaeand this is probably not the end.
According to researchers, these frogs have mastered the unusual in vertebrates art of rapid mutation and creation of new forms transforming into species. Most likely, many more will need to be described than just 35 and all in such an insignificant area. – I don’t know if we can keep up with that. Here everything is changing and it turns out that we don’t know much about frogs,” says Ivan Nunes of the University of São Paulo. Among all vertebrates, only rodents account for a larger percentage of biomass worldwide than anurans, and who knows if this view will not have to be revised as well. In Indo-Malay and Australasia and Oceania, anuran amphibians account for more than 40 percent of the total vertebrate biomass.